Hi friend!
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One of the best things abiut GrapheneOS is being able to easily restrict network access for apps. So for a camera app, you can use anything you want, even Google Camera, and just turn off network access so there is no way for Google to spy. The suggestion of OpenCamera is also good. It has a lot of power and options.
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Battery life should be just as good, more or less.
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Sandboxed play services basically means that GrapheneOS gives it fewer permissions on your phone. Normally it has a very privileged position in the OS and is fairly imvasive.
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Its user profiles are very powerful and I highky recommend using them. I recommend not installing samdboxed google play services on yiur main (owner) profile. If you do end up needing google play services for an app, it is better to put it in a separate profile.
If it is helpful, I think of Degoogling as being mostly about replacing services. Graphene is a good atep, but definitely do a checklist of Google services that you use and slowly replace them and take control over your digital spaces. I would recommend dealing with your email as a top priority. Buying a domain (use a common/safe tld) so that you own your address (e.g. [email protected]) will mean no company can ever prevent you from sending or receiving emails on a whim. Using something like fastmail to receive and send emails via your domain will be the easiest first step.